1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disk and to a recording and reproduction apparatus for recording information on an optical recording medium and detecting recorded information on an optical recording medium.
2. Description of the Related Art
In recent years, the recording densities of optical disks have been improved. Further, their formats, which determine the recording and reproduction systems, have been changed.
For example, in a 90 mm size magneto-optical disk (MO disk) of the International Organization for Standardization (ISO) standard, the first generation capacity was 128 MB, the second generation capacity 230 MB, and the third generation capacity 640 MB. The recording capacity has improved with each generation.
Similarly, in a 130 mm size magneto-optical disk, the first generation capacity was 650 MB, the second generation capacity 1.3 GB, and the third generation capacity 2.0 GB. Again, the recording capacity has improved with each generation.
The size of a beam spot of a laser beam focused on an optical disk is determined by optical parameters such as the wavelength λ of the laser beam used and the numerical aperture NA of the object lens, so the format of an optical disk is closely related with the optical parameters.
In the format of optical disks in the related art, the optical parameters have been changed along with each generation to enable recording and reproduction of finer marks using a smaller beam spot.
Also, the modulation and demodulation methods, addressing method, method of division of recording regions, etc. have been changed so as to be suited for the finer marks. For example, the zone format, the number of addresses in a zone, the recording capacity of an address, modulation method, demodulation method, etc. have been changed with every generation. As a result, the recording capacity of optical disks has been improved along with each generation.
Recording and reproduction apparatuses for third generation optical disks are designed based on these changes in first and second generation formats so as to be able to handle first, second, and third generation optical disks.
Summarizing the problem to be solved by the invention, generally, however, recording and reproduction apparatus designed for first generation optical disks cannot handle second and third generation optical disks. This is because in the first generation, it was difficult to predict the modulation and demodulation methods, addressing methods, etc. of the following generations.